Regeneration of tissue lost to disease or trauma is a goal of medicine. Such tissue losses—cartilage due to osteoarthritis, spinal nerves due to trauma, islet cells due to diabetes, cardiac muscle due to infarction, etc—cost hundreds of millions of dollars a year in addition to the lost quality of life of the patients. Embryonic stem cells have captured the news as a source of stem cells for tissue regeneration. The ethical problems are well known, but there are also less well-known problems such as tissue rejection, tumor formation, and inability to direct the differentiation of the cells.
Several research groups have been investigating the possibility of using non-embryonic stem cells, i.e., stem cells isolated from post-natal animals. The challenge associated with such stem cells is that they may not be able to differentiate in all three germ lineages, endodermal, mesodermal and ectodermal lineages. For example, the differentiation of some of the previously reported post-natal stem cells seems to be limited to mesodermal lineage. Additionally, some of the cells have a finite lifetime, which limits their usefulness when large numbers of cells are needed or if the regenerated tissue needs to last for 20 or more years.
Therefore, there is a need in the art for adult stem cells that have the ability to differentiate into all three lineages and that have indefinite propagation potential. Applicants have now isolated and characterized such cells.